leaded gas and valve-seat recession

[JHertzman@xxxxxxx]

 In AD7-397 brother Will Owen picks a nit with Papa Fred Di Matteo on the
leaded gas question. Fred was talking about Alfas, and Will countered with a
report on a carefully controlled British test on a British vintage-design
engine (I believe from the Edwardian era, definitely post-Watt but probably
before tetraethyl lead was discovered) which has found valve-seat recession of
1 to 1.2 mm in a 70 hour cycle when run without leaded gas. Assuming a 30 mph
average on "B" roads, that would be about 2,000 miles. Over say 100,000 miles
the 1 to 1.2 mm in a 70 hour cycle would work out to a valve seat recession of
a bit over two inches, increasing combustion chamber volume to the point where
octane rating would no longer be an issue. 

I do remember tales of prewar (not saying which war) break-in instructions
which included removing the head for de-coking and valve grinding 250 miles
after delivery, and periodically thereafter at relatively short intervals-
every thousand miles comes to mind. I was never quite sure whether this was a
dead-pan elaboration on the traditional Lucas joke. However, the fact remains
that Alfa, with separate seats in alloy heads, can use materials which might
not be suitable for an all-in-one casting of a traditional iron head. More to
the point, for whatever reason, valve seat recession with unleaded fuel
doesn't seem to be that serious a problem in any Alfa engine designed within
living memory.

Cordially,

John H.
Raleigh N.C.

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